Motion detection is an important feature in intelligent lighting systems, which are activated when the presence of people is detected. A common and relatively cheap sensor for motion detection is the passive infrared (PIR) sensor. A conventional PIR sensor comprises a pyroelectric element, which generates a temporary voltage when it is heated or cooled, and a Fresnel lens (or other optical means) for focusing infrared (IR) radiation from a certain area (the sensing region of the PIR sensor) on the pyroelectric element. Typically, two or four pyroelectric elements are wired as opposite inputs to a differential amplifier to cancel increases of IR energy across the entire sensing region caused by a general temperature increase in the sensing region.
Commonly available PIR sensors are normally binary sensors, i.e., they can detect whether a heat source is present or not in the sensing region of the PIR sensor, but they cannot determine the position of the heat source within the sensing region. US 2009/0219388 shows a PIR sensor system comprising four PIR sensors focusing on the same area of observation, in which the field of vision is modulated and coded. To do this, for each of them, a combination of lenses, and thus beams, is masked. The combination is different for each sensor in order to associate a unique code with each beam and to provide data to locate a position and movement of a heat source. However, such a PIR sensor system has the drawback that custom-made masking elements have to be designed and installed for each sensor, which implies high production and installation costs. Further, all the PIR sensors have to focus on the same area, which implies that several PIR sensors have to be added to a standard presence detection system to achieve the position and movement detection functionality.